The present invention relates generally to a coalescing filter element for a compression system. In particular, the present invention relates to an oil coalescing filter element having a drainage mechanism to reduce the amount of oil entrained in the filter media.
Positive displacement compressors are machines in which successive volumes of air or gas are confined within a closed space and elevated to a higher pressure. The pressure of the gas is increased while the volume of the closed space is decreased. Positive displacement compressors include, for example, reciprocating compressors, rotary compressors, scroll compressors and screw compressors. These compressors rely on lubricating oil to lubricate rotating and contacting surfaces to allow for efficient operation, to prevent damage to the units and to seal the volume being compressed.
For example, a screw compressor generally includes two cylindrical rotors mounted on separate shafts inside a hollow, double-barreled casing. The side walls of the compressor casing typically form two parallel, overlapping cylinders which house the rotors side-by-side, with their shafts parallel to the ground. Screw compressor rotors typically have helically extending lobes and grooves on their outer surfaces forming a large thread on the circumference of the rotor. During operation, the threads of the rotors mesh together, with the lobes on one rotor meshing with the corresponding grooves on the other rotor to form a series of gaps between the rotors. These gaps form a continuous compression chamber that communicates with the compressor inlet opening, or port, at one end of the casing and continuously reduces in volume as the rotors turn and compress the gas toward a discharge port at the opposite end of the casing. Lubricant is introduced into the compressor at a relatively constant rate from a lubricant circulation system to lubricate the rotor shafts, bearings and seals, to help seal the clearances between the screws during operation of the compressor, and to help remove the heat of compression, thereby preventing the compressor from overheating and to help reduce the noise associated with compressor operation.
Lubricants typically are some type of oil-based liquid compound, this part of the compressor system often being referred to simply as the “lube-oil” system. Compressor lube-oil systems generally include a collection reservoir, filter, and pressure and/or temperature sensors. The lube-oil may be circulated as a result of the pressure differential in the system across the evaporator and condenser, such as in water chiller screw drive compressor systems, or the lube-oil may be circulated by a motor driven pump such as in larger reciprocating compressors. Since many lubricants degrade at high temperature by losing viscosity, compressors operating at high temperatures, such as with screw compressors, generally include specially formulated lube-oil systems and also include a cooler for reducing the temperature of the lubricant before it is recirculated to the seals and bearings. So-called “oil flooded” screw compressors may further include means for recirculating lubricant through the inside of the compressor casing. Such “lube-oil injection” directly into the gas stream has been found to help cool and lubricate the rotors, block gas leakage paths between or around the rotors, inhibit corrosion, and minimize the level of noise produced by screw compressors.
As is evident in these positive displacement type compressors, lubricant and fluid in the gaseous state are mixed as a result of compressor operation. Under these high pressures and temperatures, the lubricant forms droplets of various sizes. These droplets typically are entrained in the gas stream and must be removed before the compressed gas is transported away from the compressor. To prevent the lubricant entrained in the gas stream from moving downstream, a separator section can be used. The compressed gas may be forced to follow a tortuous path or contact a surface where larger droplets can agglomerate and can be cycled back into a sump-type device for reuse, lubricating the moving parts of the compressor. To capture the finer aerosol droplets that are not agglomerated into droplets of sufficient size to be separated, the separator section typically employs a coalescer or filter unit through which the compressed gas and aerosol must pass before being discharged downstream of the separator. However, one problem with the use of the coalescer or filter unit is that the captured lubricant remains and accumulates in the coalescer or filter unit thereby reducing the amount of area of the coalescer or filter unit that can be used to capture lubricant.
Therefore, what is needed is a mechanism for a coalescer or filter element that can facilitate the drainage of the captured lubricant from the coalescer or filter element.